The braking systems of heavy vehicles are normally pneumatically operated. In general, such pneumatic braking systems comprise a compressor for pressurizing air, and two lines between the compressed air reservoir and the brakes. A first line, the so-called supply line, pressurises the braking system. In the event that the supply line is disconnected or severed, or air pressure for other reasons is released from the supply line, the vehicle's brakes are designed to engage automatically. A second line, the so-called control line (also referred to as a pilot line), controls the air pressure acting on the respective brakes and operates the mechanical parts in the brake. The control line pressure is controlled by the brake pedal valve. When the driver operates the brake pedal in the driver's cabin, pressure in the control line will increase, and act on valves in the braking system of the trailer to activate the brakes controllably and in proportion to the force exerted on the brake pedal.
In a tractor-trailer unit (e.g. a lorry or similar, pulling a trailer), the trailer is also equipped with a pneumatically operated braking system. The pneumatic braking system of a trailer also comprises a supply line and a control line, both of which are connected to the tractor's supply line and control line via a connector. (The connector is commonly of a standardised type, well known in the industry, for example “duomatic” or “glad-hands”). Thus, when the driver operates the brake pedal, both the tractor's brakes and the trailer's brakes are operated simultaneously. At the same time, brake lights are lit both on the rear of the tractor and the rear of the trailer.
In order to gain knowledge of how much braking power the tractor-trailer unit develops, one needs to know the pressure of the air which is sent from the brake pedal to the individual wheel brakes. This pressure may be measured at i.a. the connection between the tractor and the trailer.
Tractor-trailer units must comply with rigorous technical requirements, in order to be considered safe for operation on public roads. One such technical requirement is the operability and quality of the brakes (e.g. the mechanical parts, the pneumatics operating the mechanical parts, and associated control systems). Even minor deficiencies in the brakes may lead to reduction in braking power, thus increasing the stopping distance beyond acceptable and mandatory values. A technical test of the brakes in a tractor-trailer unit is normally performed by means of braking tests in a test stand or by measuring the deceleration when braking on the open road or on a test track. Such deceleration is measured in a known fashion, e.g. by accelerometers installed on the vehicle.
It is normally a simple task to control the brakes on the tractor (e.g. lorry, truck) by itself, by e.g. disconnecting the trailer and conducting deceleration measurements when applying the brakes. Performing brake tests on a trailer, however—be it a conventional trailer or a semi-trailer, is a much more complex task with today's technology. State-of-the-art braking systems include automatic and electronic systems (ABS, EBS) whereby the braking action on the trailer is adapted to the braking action on the tractor, and vice versa. Effecting the brakes on the trailer only (and not the tractor) while the tractor-trailer unit is moving (i.e. regular driving mode on the road), has proven difficult without considerable modifications to the vehicles and/or the assistance of additional personnel. There thus is a long felt need for an efficient and simple device and method of testing trailer and tractor units independently of one another, while the tractor-trailer unit is driving.
The state of the art includes GB 2 361 975 A, which describes a device for testing the electrical and pneumatic systems of a stand-alone and stationary trailer unit, comprising input lines for supply of compressed air and electrical power, output means adapted to transfer pneumatic pressure and electrical power to a trailer unit, and a control means, wherein a handheld remote control unit is provided. The handheld remote control unit is adapted to transmit signals to a receiver in the device, and the control means are adapted to be actuated by said signals relayed by said receiver means to control said output means in response thereto.
The state of the art also includes U.S. Pat. No. 6,530,261 B1, describing an apparatus (and an associated method) for testing air brakes of stand-alone and stationary trailers, and including a portable air-brake governing or actuation system and a hand-held control pendant, operating off an independent compressed air supply. Without the coupling of, and connections to, a tractor, the air brakes of a trailer can be applied and released, and held in a charged mode for a period of time during which any loss of air pressure can be monitored.
The state of the art thus describes testing of the pneumatic lines of brake systems in a static state, i.e. while the trailer is stationary.
The present applicant has devised and embodied this invention to overcome these shortcomings and to obtain further advantages.